The causes of systemic lupus erythematosus (SLE) are unknown, however, the pathogenesis is attributed, at least in part, to T-cell dysfunction. Preliminary studies reveal activation of the mechanistic target of rapamycin complex 1 (mTORC1) in lupus T cells which precedes disease flares and causes pro-inflammatory lineage specification in SLE patients. Upstream of mTORC1, depletion of reduced glutathione (GSH), enhanced production of reactive oxygen intermediates (ROI), and defective mitophagy are newly identified. Outcomes of a double-blind placebo-controlled clinical trial show that therapeutic reversal of GSH depletion by N-acetylcysteine (NAC) blocks mTORC1 in vivo. Therefore, the proposed studies will address a critical knowledge gap by determining how metabolic pathways that control oxidative stress and normal T-cell development contribute to lupus pathogenesis. The central hypothesis is that primarily GSH depletion drives the pathogenesis of SLE through mTORC1-dependent expansion of pro-inflammatory T cells. The rationale for the proposed research is that, after elucidating the genetically controlled metabolic pathways that promote GSH depletion and mTORC1 activation and thus trigger lupus pathogenesis, new and potentially synergistic approaches can be used for prevention and treatment of SLE. Guided by compelling preliminary data, our hypothesis will be tested in three Specific Aims: 1) to delineate the metabolic program that causes the accumulation of oxidative stress-generating mitochondria in lupus T cells; 2) to identify the role of GSH depletion in mTORC1-dependent T-cell lineage specification in longitudinal studies of SLE patients; and 3) to determine the role of GSH depletion in the pathogenesis of systemic autoimmunity in lupus-prone mice. Under Aim 1, S-nitrosylation of ND3 subunit in complex I of the electron transport chain and lupus-linked mitochondrial DNA (mtDNA) polymorphisms in ND2 and ATP6 will be assessed as causes of increased ROI production. Under Aim 2, GSH depletion and mTORC1 activation will be genetically targeted in vitro for reversing pro-inflammatory T-cell development focusing on CREM-a/IL-4-mediated trans-differentiation of CD8 T cells to DN T cells and HIF1a/IL-17-mediated depletion of Tregs in SLE patients. Under Aim 3, GSH depletion will be modeled by the inactivation of transaldolase and evaluated as a cause of disease pathogenesis in lupus-prone mice. The proposed research is significant because it will advance our understanding of T-cell lineage development in normal and autoimmune conditions with relevance for identifying new treatment targets in SLE. The approach is innovative as it departs from the status quo by utilizing metabolic pathway genes to regulate T-cell development. The results will open new horizons in our understanding of the metabolic pathways that control oxidative stress and its role in disease pathogenesis while providing new mechanistic targets for treatment of SLE.